1. Field of the Invention
The invention relates to a boat propulsion improved in acceleration.
2. Related Art
As disclosed in the Japanese Laid Open Gazette No. Hei 10-194196, there is a well-known conventional boat propulsion system having a pair of hydraulic clutches for forward propelling and backward propelling on its drive train between an engine and a propeller shaft.
The conventional system as disclosed in the document includes first, second and third shafts. The first shaft is coupled to a flywheel of the engine. The second shaft is disposed in parallel to the first shaft and drivingly connected to the first shaft through meshing gears fixed on the respective shafts so as to rotate opposite to the first shaft. The meshing gears between the first and second shafts do not serve as a deceleration gear, i.e., the gear ratio therebetween is 1:1. The third shaft serves as the propeller shaft. Each of the first and second shafts is provided thereon with a gear constantly meshing with a gear fixed on the third shaft. Each of the hydraulic clutches is interposed between the gear on the third shaft and the gear on each of the first and second shafts. One of the hydraulic clutches is selectively engaged to connect the corresponding gear and shaft, thereby drivingly coupling one of the first and second shafts to the third shaft, that is, propelling a boat either forward or backward.
However, the above conventional boat propulsion system has a problem. When the stationary propeller shaft is beginning acceleration, i.e., when the hydraulic clutch is engaged and the engine in idling at full-throttle, the resistance of the water against the rotating propeller fixed on the propeller shaft is transmitted to the engine through the engaging hydraulic clutch and the like, so as to prevent smooth acceleration of the engine. This is the reason why the boat equipped with the conventional propulsion system in stationary cannot be smoothly accelerated to get a desired high speed.